Control system

ABSTRACT

A control system for regulating the performance of predetermined sequences of operations by an operating device upon sheets of material having variable lengths is disclosed in accordance with the teachings of the present invention wherein photoelectric sensing means are utilized to sense the leading and trailing edges of a sheet of material upon which the device operates. Pulse generating means generates first and second pulses when the photoelectric sensing means senses the leading and trailing edges respectively, of a sheet of material. First and second switch means respond to the generated first and second pulses for initiating first and second predetermined sequences of operations respectively, to be performed by the operating device.

United States Patent 1191 Gerace 1 Dec. 25, 1973 CONTROL SYSTEM 3,480,762 11/1969 Delvecchio 250/219 DC Inventor: Robert E. Gerace, Fairport, N.Y. 3,114,841 12/1963 Paananen 250/223 [73] Assignee: Xerox Corporation, Stamford, Primary Examiner-James W. Lawrence Conn. Assistant Examiner--D. C. Nelms Attorney-James J. Ralabate, Michael J. Collitz, Ber- [22] Flled' 1971 nard .I. Lacomis and Michael H. Shanahan [21] App]. No.: 131,114

[57] ABSTRACT [52] US. Cl. 250/206 R, 250/223 R A control system for regulating the performance of [51] Int. Cl. HOlj 39/12 predetermined sequences of operations by an operat- [58] Field of Search 250/221, 214, 222, ing device upon sheets of material having variable 250/223, 219 DC, 2 9 206 lengths is disclosed in accordance with the teachings 209/1 1 1 355/14 of the present invention wherein photoelectric sensing means are utilized to sense the leading and trailing [56] References Cited edges of a sheet of material upon which the device op- UNITED STATES PATENTS erates. Pulse generating means generates first and sec- 3 677,635 7/1972 Vanauken 355/14 ond Pulses when Phmoelectric sensing means 31501136 3/1970 Maloney 355/14 Senses the leading and trailing edges respectively, Of a 3,604,796 9/1971 Ogawa 355/14 sheet of ate i F rst and second switch means re- 3,673,4l4 6/1972 Taniguchi 307/311 spond to the generated first and second pulses for ini- 3,320,430 5/1967 Gorman 307/311 tiating first and second predetermined sequences of 3,543,035 11/1970 Raye r 250/222 operations respectively to be performed the pe 3,114,902 12/1963 Tanguy 250/223 ating device 3,430,052 2/1969 Stephan 250/222 2,738,448 3/1956 Bokser 250/221 12 Claims, 4 Drawing Figures Monosiuble Mechanical l' Multivibrotor clutch I a I Programmer ,0 Schmitt 7, Pulse Tngger Gen.

Motor Drive '20 2 opemm'g system 3 Device Monosiuble Mechanical Multlvibrotor l l Programmer I PATENTEU UEC 2 5 i973 SHEET 2 (If 3 INVENTOR.

Robert E. Geroce 772mm &

ATTORNEYS 838.80 33m :52; E g m CONTROL SYSTEM This invention relates to a control system forregulating the performance of predetermined sequences of operations by an operating device and more particularly, to a control system for controlling the operation of a device in accordance with the length of a sheet of material upon which .said device operates.

Many devices that perform operations upon sheets of material require that such operations be executed in a predetermined sequence. Exemplary devices include industrial assembly machines wherein sheets .of mate= rial are transported to various mechanisms for manufacturing a completed product, data card readers and perforators, and document reproducing machines. In each of the aforementioned devices the operations performed on the sheet of material, i.e., a sheetof industrial material, a data card or a document, are usually performed in a predetermined timed sequence. Unfortunately a variation in the length of the material upon which the operations are performed, or a variation in the operating speed of the machine results in an im-' properly timed operation. Although the prior. art has attempted to minimize variations in machine operating speed by rigid synchronization-thereof, variations in the length of the sheet of material have heretofore required corresponding manual adjustments of the device to facilitate proper performance of each sequence of operations.

To facilitate the explanation thereof the present invention will be described with reference to its application in an electrophotographic reproducing device. However, it will be understood that the subject matter of the present invention is readily applicable to other devices such as the exemplary devices mentioned-here inabove.

The disclosure of electrophotographic reproduction in US. Pat. No. 2,297,691 which issued'to C. F. Carlson has resulted in a variety of commercially available reproducing devices. Most of these devices produce a copy of an original document by depositing an electrostatic charge on the surface of a photoreceptor, advancing the charged photoreceptor to an exposure station whereat the charged photoreceptor is exposed to an image of said original document, advancingthe exposed photo'receptor to a developing station whereat the electrostatic latent image of the original .document is developed by depositing toner particles thereon, advancing the developed photoreceptor to a'transfer station whereat the developed image is transferred to a support surface, advancing the support surface through a fusing station whereat the transferred developed image is fused to the support surface thereby forming a copy of the original document, and advancing the copy to an external location. The aforementioned steps are performed sequentially under the control of pre-set programming means. The tpre-set programming means may comprise electrical apparatus such as a wellknown digital computer, or the pre-set programming means may comprise mechanical apparatus s'uchas rotatable cam assemblies which are described in U. S. Pat. No. 3,301,126 which issued to R. F. Osborne et al. on Jan. 31, 1967 and assigned to Xerox Corporation. The electrophotographic reproducing device disclosed in the last-mentioned patent includes a transportable exposure station adapted to scan a stationary document. In addition .the developed electrostatic latent image is transferred to individual sheets of paper. An alternative embodiment of an electrophotographic rcproducing device is disclosed in U. S. Pat. No. 3,401,613 which issued to M. Davis on Sept. 17, 1968 and assigned to Xerox Corporation wherein an original document is transported past a fixedly disposed exposure station and the developed electrostatic latent image is transferred to a web of paper. The Davis patent discloses means for cutting a support surface web in spaced relation to the leading and trailing edges of the original document being reproduced. However the essential operations described hereinabove are executed independently of the length of the document.

The prior .art has attempted to regulate the operations of an electrophotographic reproducing device in accordance with the length of a document to be reproduced by disposing microswitches in the transport path of the document. The microswitches are adapted to energize appropriate circuits when the'document is in contact therewith. An attendant disadvantage however is the unreliability of micro-switch operation. Repeated actuation of the micro-switch results in frequent failure thereof. In addition physical contact between the micro-switch and the document to be reproduced often results in deformation of the document which may inutilate the document and obstruct the machine.

Therefore, it is an object of the present invention to provide a control system for regulating the performance of predetermined sequences of operations by an electrophotographic reproducing machine in accordance with the length of the'document to be reproduced.

It is another object of this invention to provide apparatus for activating the mechanical programmers of an electrophotographic reproducing device such that a first sequence of operations is performed upon sensing the leading edge of document to be reproduced and a second sequence of operations is performed upon detecting the trailing edge of a document to be reproduced.

It is a further object of this invention to provide a control system including photoelectric sensing means for sensing the leading and trailing edges of a document to be reproduced, for regulating the performance of predetermined sequences of operations.

Yet another object of this invention is to provide apparatus for activating the mechanical controlling means of a device wherein said device performs sequential operations upon sheets of material having variable lengths.

A still further object of this invention is to provide a control system for creating delays in the performance of sequential operations by an electrophotographic reproducing machine wherein said delays correspond to the length of the document to be reproduced.

An additional object of this invention is to provide a control system for regulating delayed operation of an electrophotographic reproducing machine wherein said control system is operable independent of the mechanical drive speed of said machine, and said drive speed need not be constant.

Another object of this invention is to initiate the operation of a device upon sensing the leading edge of a sheet of material upon which said device operates and to terminate the operation of said device upon detect .ing the trailing edge of said'sheet of material.

Various other objects and advantages of the invention will become clear from the following detailed description of exemplary embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with this invention a control system for regulating the performance of predetermined sequences of operation by an electrophotographic reproducing machine in accordance with the length of a document to be reproduced is provided wherein photoelectric sensing means senses the leading and trailing edges respectively, of the document to be reproduced; pulse generating means coupled to said photoelectric sensing means generates first and second pulses in response to the sensing of the leading and trailing edges respectively; first switch means responds to a generated first pulse for activating a mechanical programming means to control a first predetermined sequence of operations; and second switch means responds to a generated second pulse for activating the mechanical programming means to control a second predetermined sequence of operations.

The invention will be more clearly understood by reference to the following detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a first embodiment of the control system of the present invention;

FIG. 2 is a schematic diagram of aportion of the apparatus of FIG. 1;

FIG. 3 is a block diagram of another embodiment of the control system of the present invention; and

FIG. 4 is a schematic diagram of a portion of the apparatus of FIG. 3.

Referring now to the drawings wherein like reference numerals are used throughout, and in particular to FIG. 1, there is illustrated a block diagram of an embodiment of the control system of the present invention which. I comprises photoelectric sensing means 10, Schmitt trigger means 13, pulse generating means 14, monostable multivibrator means 16 and 17, clutch means 18 and 19, mechanical programming means 21 and 22and.device23.' As noted hereinabove, the present invention will be described with reference to an electrophotographic reproducing device. Accordingly,

device 23 may comprise a conventional electrophotographic device. It is understood however that device 23 may comprise a data card reader, a data card perforator, an industrial assembly machine or any other device adapted to perform operations on sheets of material. Photoelectric'sensing means 10 may comprise a conventional photocell such as a phototransistor, a photodiode or the like, or a phototube adapted to produce an output signal having a magnitude proportional to the intensity of radiation impinging thereon. Accordingly photoelectric sensing means 10 is spaced from and in optical communication with a source of light 11. The

cept the optical path between the source of light 1 l and the photoelectric sensing means 10.

Photoelectric sensing means 10 is coupled to pulse generating means 14 via Schmitt trigger means 13. The Schmitt trigger means 13 is a well-known triggerable bistable circuit adapted to provide an indication of the relative magnitude of an input signal supplied thereto. Accordingly, Schmitt trigger means I3 is capable of assuming a first stable state represented by a signal admitting of a first level 'whenthe output signal supplied thereto by photoelectric sensing means 10 exceeds a predetermined threshold level and a second stable state represented by a signal admitting of a second level when the output signal supplied thereto by the photoelectric sensing means 10 is less than the predetermined threshold level. Schmitt trigger means 13 may be replaced by other conventional level detecting circuits, such as an amplitude comparator or a unijunction transistor circuit, adapted to indicate whether the magnitude of the signal produced by photoelectric sensing means 10 exceeds a, predetermined threshold level. Pulse generating means 14 includes a first output terminal coupled to monostable multivibrator means 16 via inverting circuit 15 and a second output terminal coupled to monostable multivibrator means 17. The pulse generating means 14 is adapted to detect a change in the stable state assumed by Schmitt trigger means 13. Accordingly, pulse generating means 14 is responsive to a transition in the level of the signal applied thereto by Schmitt trigger means 13. One embodiment of pulse generating means 14 may comprise a conventional differentiating circuit whereby a pulse is produced at a first output terminal thereof in response to a transition from the second level to the first level in the signal supplied thereto and a pulse is produced at a second output terminal thereof in response to a transition from the first level to the second level in the signal supplied thereto. Alternatively, pulse generating means 14 may include a single output terminal whereat a positively poled pulse is produced in response to a positive transi tion in the signal supplied thereto and a negatively poled pulse is produced in response to a negative transition in the signal supplied thereto. Another embodiment of pulse generating means 14 may comprise a conventional univibrator circuit; It should be understood by those skilled in the. art that Schmitt trigger means 13 and pulse generating means 14 may be combined in a single circuit such as a unijunction transistor circuit or the like whereby a first pulse is generated when the magnitude of the signal produced by photoelectric sensing means 10 exceeds a predetermined threshold level and a second pulse is generated when the magnitude of the signal produced by photoelectric sensing means 10 is less than said predetermined threshold level.

Monostable multivibrator means 16 is a conventional bistate device exhibiting a stable output state and a quasi-stable output state. The monostable multivibrator means 16 may be triggered into the quasi-stable output state thereof upon applying a pulse thereto. As is understood by those skilled in the art, the monostable multivibrator means 16 assumes its quasi-stable output state for a period of time determined by the time constant thereof. Accordingly, the monostable multivibrator means 16 serves to provide an output pulse of uniform pulse width in response to each input pulse applied thereto. It will be seen hereinafter that monostable multivibrator means 16 may be triggered into its quasistable state by applying a negative going pulse thereto. However pulse generating means 14 is adapted to provide a positively poled pulse at the first output terminal thereof in response to a positive transition in the signal supplied thereto. Accordingly, inverting circuit 15 is interposed between pulse generating means 14 and monostable multivibrator means 16 to invert the polarity of the triggering pulse. inverting circuit 15 may comprise a conventional inverting amplifier, a phase inverter or a logic negation circuit, well known to those of ordinary skill in the art. It is of course recognized that if monostable multivibrator means 16 is adapted to be triggered into its quasi-stable state by a positively poled triggering pulse, inverting circuit 15 may be omitted. Monostable multivibrator means 17 is coupled to the second output terminal of-pulse generating means 14 and is identical to the aforementioned monostable multivibrator means 16. Accordingly, further description of monostable multivibrator means 17 need not be set forth herein. Since a negatively poled triggering pulse is provided at the second output terminal of pulse generating means 14 in response to a nega-. tive transition in the signal supplied thereto, it is not necessary to interpose an' additional inverting circuit between the pulse generating means 14 and the monostable multivibrator means 17. 2

Monostable multivibrator means 16 is coupled to clutch means 18 and is adapted to activate the latter upon assuming its quasi-stable output state. Accordingly clutch means 18 may include electromagnetic means such as solenoid means, relay means, a combination thereof, or thelike. Activation of clutch means 18 is effective to couple mechanical programming means 21 to the motor drive system 20 of device 23. Mechanical programming means 21 may comprise a first rotat= able cam assembly such as described in U. S. Pat. No. 3,301,126 which issued on Jan. 31, 1967 to R. F. Osborne. Coupling of the first cam assembly 21 to the motor drive system 20 enables each of the cams therein source of light 11, the photoelectric sensing means responds to the relatively high intensity ofimpinging light to rotate in synchronism with the motor to thereby control a first sequence of operations performed by device 23.

Clutch means 19 is coupled to monostable multivibrator means 17 and is adapted to be activated upon the assumption of the quasi-state output state thereof I FIG. 1 will now be described with reference to a conventional electrophotographic reproducing device. It is recalled however that the present invention finds ready application with any device capable of performing operations upon sheets of material having variable lengths. Initially photoelectric sensing means 10 receives a beam of light of substantially constant intensity communicated thereto from the source of light 11. If it is assumed there is no obstruction in the light path defined by the photoelectric sensing means 10 and the to produce a signal that is less than a predetermined threshold level. This signal is applied to Schmitt trigger means 13 whereby the Schmitt trigger means assumes a second stable state which is represented by a signal admitting of a second level. As is understood by those of ordinary skill in the art, the signal representative of the state of Schmitt trigger means 13 is a dc. signal.

It is recalled that the pulse generating means 14 is responsive to transitions in the signal supplied thereto. However the signal presently supplied by Schmitt trigger means 13 admits of a constant d.c. second level. Accordingly'trigger pulses are not provided at the first and second output terminals of pulse generating means 14 and monostable multivibrator means 16 and 17 maintain their respective stable output states. Thus, neither clutch means 18 nor clutch means 19 is activated and neither mechanical programming means 21 nor mechanical programming means 22 is coupled to motor drive system'20. Consequently, device 23 will not execute the sequences of operations that are controlled by the mechanical programming means 21 and 22 respectively, and device 23 will maintain a quiescent condition.

It will now be assumed that a document to be reproduced 12' is introduced into the space defined by photoelectric sensing means 10 and the source of light 11. It'

is recognized that the document, 12 may be transported in the direction indicated by the arrow A by conventional transport means such as a conveyor belt, drive rollers or the like. Alternatively, the document 12 may assume a stationaryv relationship .and an exposure mechanism including the photoelectric sensing means 10 and source of light 11 may be displaced in a direction opposite to that indicated by the arrow A to scan the surface of the document. in either event when the leading edge of document 12 intercepts the optical path between the source of light 11 and photoelectric sensing means 10, the obstruction presented thereby reduces the intensity of light impinging on the photoelectric sensing means 10 to a substantially zero value. Accordingly, the signal applied by the photoelectric sensing means 10 to Schmitt trigger means 13 increases to exceed the predetermined threshold level. Schmitt trigger means 13 responds to the signal applied thereto to assume the first stable state thereof, 'which state is represented by a signal admitting of a first level. Thus, the d.c. signal supplied to pulse generating means 14 is now characterized-by a transition from a second level to a first-level. If it is assumed that the first level of the d.c. signal supplied to pulse generating means 14 is greater than the second level thereof, pulse generating means 14 is actuated to generate a positive pulse at the first output terminal thereof in response to the positive transition. The polarity of the positive pulse is inverted by inverting means 15 thereby applying a negative triggering pulse to the input terminal of monostable multivibrator means 16. It is of course recognized that if monostable multivibrator means 16 is operable in re-- sponse to the triggering pulse applied thereto, a pulse of predetermined width is applied to clutch means 18. If the clutch means 18 includes an electromagnetic member, such as a solenoid, the pulse applied thereto enables the solenoid to be energized, thereby releasing a mechanical clutch member such as a spring clutch. It is clear then that when monostable multivibrator means 16 returns to thestable output state thereof, the result- I ing de-energization of the-solenoid will have no effect upon the released clutch member. Release of the mechanical clutch member couples the mechanical programming means 21 to motor drive system 20 whereby the cam assembly includable in the mechanical programming means 21 now rotates in synchronism with the motor. As the cam assembly rotates, a first sequence of opcrationsis performed by the device 23. Typical of these operations are:- the charging of a photoreceptor initiated by the rotation of a first cam; exposure of the charged photoreceptor to a light image of the document 12 to form an electrostatic latent image, initiated by the rotation of a second cam; development of the electrostatic latent image, initiated by the rotation of a third cam; transfer of the developed image-to a web, initiated by the rotation of a fourth cam; and movement of the web, initiated by the rotation of a fifth cam. It is recognized that the foregoing operations are merely exemplary of some of the operations performed by a conventional electrophotographic reproducing device, and are not to be interpreted as limiting the present invention thereto. In addition the sequence of performance of the foregoing operations is not limited to the sequence just described and is determinable by the particular mechanical programming means utilized.

As the document 12 continues to be transportedin a direction indicated by the arrow A, the intensity of the light impinging upon photoelectric sensing means 1 is substantiallyconstant. Accordingly Schmitt trigger means 13 is supplied with a signal that is maintained above the predetermined threshold level and the Schmitt trigger means retains the first stable state thereof. Consequently pulse generating means 14 does not detect further transitions in the d.c. signal supplied thereto and additional triggering pulses are notgenerated thereby. Hence monostable multivibrator means 16 and 17 assume their respective stable output states and clutch means 18 and 19 are not activated. The normal operation of mechanical programming means 21, once initiated, is therefore not affected and device 23 performs a first sequence of operations. When the trailing edge of document 12 is transported past the optical path defined by the source of light 11 and photoelectric sensing means 10, the intensity of the light impinging upon photoelectric sensing means 10 is increased such that the signal supplied to Schmitt trigger means 13 falls below the predetermined threshold level. Consequently Schmitt trigger means 13 assumes the second stable state thereof and the d.c. signal now supplied to pulse generating means 14 is characterized by a negative transition from the aforementioned first level to the second level. Pulse generating means 14 responds to the negative transition to generate a negatively poled triggering pulse at the second output terminal thereof, which pulse is applied to monostable multivibrator means 17. Application of the triggering pulse to mono stable multivibrator means 17 triggers the monostable multivibrator means into the quasi-stable output state thereof, thereby applying a pulse of predetermined width to clutch means 19. As is now understood, clutch means 19 is thus activated to couple mechanical programming means 22 to motor drive system 20. The ensuing rotation of the cam assembly comprising mechanical programming means 22 controls a second sequence of operations executed by device 23. Typical of these operations are: fixing of the transferred image to the web, initiated by the rotation of a first cam; cutting of the web, initiated by the rotation of a second cam; delivery of the copy to a location external of the electrophotographic reproducing device, initiated by the rotation of a third cam; and preparing the device for subsequent operation, initiated by the rotation of a fourth cam. The foregoing operations and sequence of execution thereof are merely exemplary and are not intended to limit the use of device 23 or the application of the present invention. Other operations may be performed and in a sequence determined by the particular programming means utilized.

It is to be understood that when the programs determined by mechanical programming means 21 and 22 respectively, are completed, clutch means 18 and 19 are restrained from further rotation, thereby decoupling the respective mechanical programming means from motor drive system 20.

The control system illustrated in FIG. 1 is subject to 'various modifications and changes. For example, the

photoelectric-sensing means. 10 may produce a signal that is less than a predetermined threshold level when document 12 is interposed in the optical path defined by the source of light 11 and the photoelectric sensing means 10, whereupon Schmitt trigger means 13 assumes its first stable state. In addition, the d.c. signal supplied to pulse generating means 14 by Schmitt trigger means 13 may be characterized by a negative tran sition when photoelectric sensing means 10 detects the leading edge of document 12. Furthermore, the pulse generating means 14 may be provided witha single output terminafc onnected in common relationship to in vetting circuit 15 and monostable multivibrator means 17 to which are provided positively and negatively poled pulses. Although the foregoing and various other modifications are readily attained, it is manifest that mechanical programming means 21 be activated upon detection of the leading edge of document 12 and mechanical programming means 22 to be activated upon detection of the trailing edge of document 12.

Referring now to FIG. 2 there is illustrated a schematic diagram of a portion of the control system of FIG. 1 comprising photoelectric sensing means 10, Schmitt trigger means 13, pulse generating means 14, inverting circuit 15, monostable multivibrator means 16 and 17, and clutch means 18 and 19. Photoelectric sensing means 10 is illustrated as a variable impedence means having an impedance that varies as a function of the intensity of light impinging thereon. Hence the impedance of photoelectric sensing means 10 tends to decrease as the intensity of light communicated thereto increases and conversely, the impedence thereof tends to increase as the intensity of light decreases. A first terminal of the photoelectric sensing means 10 is coupled to terminal 103 via adjustable contact 102 of potentiometer 101. Another terminal of the photoelectric sensing means 10 is coupled to a common conducting lead adapted to be supplied with a reference potential such as ground potential. Terminal 103 is supplied with an operating potential represented as +V. Adjustablecontact 102 is additionally coupled to the Schmitt trigger means 13 via current limiting resistance 104. The Schmitt trigger means 13 is comprised of transistors 131 and 136 which are adapted for regenerative operation. The emitter electrodes of transistors 131 and 136 are connected in common to common conducting lead 105 via resistance 138. The collector electrode of transistor 131 is connected to the base elec trode of transistor 136 via the parallel circuit comprised of resistance 133 and capacitance 134. The base electrode of transistor 136 is additionally connected to common conducting lead 105 via resistance 135. The collector electrodes of transistors 131 and 136 are connected to resistances 13 2 and 137 respectively, which in turn are supplied with operating potential +V. One of ordinary skill in the art will recognize that Schmitt trigger means 13 as herein illustrated is of conventional design and is described in the sixth edition of the transistor manual published in 1962 by the General Electric Company. If desired other conventional circuits may be utilized to form the Schmitt trigger means 13.

The collector electrode of transistor 136 is connected to pulse generating means 14 which comprises first and second differentiatingcircuits. A first differentiating circuit is comprised of the series connections of capacitance 141, capacitance 145, and resistance 150 which is coupled to common conducting lead 105. The common junction of capacitance 141 and capacitance 145 is connected to common conducting lead 105 via positively poled diode 143. The second differentiating circuit is comprised of the'series connections of capacitance 142, capacitance 146 and resistance 147 which is coupled to common conducting lead 105. The common junction of capacitance 142 and capacitance 146 is coupled to the common conducting lead 105 via negatively poled diode 144. As is understood by those of ordinary skill in the art, the presence of positively poled diode 143 limits the operation of the first differentiating circuit such that positive pulses are generated across resistance 150 whereas negative pulses are inhibited. Conversely the presence of negatively poled diode 144 limits the operation of the second differentiating circuit such that negative pulses are generated across resistance 147 and positive pulses are inhibited. It is recognized that the combination of capacitance 141 and diode 143 and the combination of capacitance 142 and diode 144 comprise conventional clamping circuits.

The common junction of capacitance 145 and resistance 150, which corresponds to the aforementioned first output terminal of pulse generating means 14, is coupled to inverting means 15. inverting circuit 15 is comprised of transistor 151, arranged in emitter follower configuration, having an emitter electrode connected to the base electrode of transistor 156 via a.c. coupling capacitor 153. Transistor 156 is arranged in conventional inverting amplifier configuration for amplifying the magnitude of and inverting the sense of a pulse applied to the base electrode thereof. Resistances 154 and 155 comprise conventional biassing resistances for the transistor 156. The collector electrode of transistor 156 is coupled to monostable multivibrator means 16 via diode 161. The diode 161 is suitably poled so that monostable multivibrator 16 is triggered to its quasi-stable output state by the application of negative pulses.

Monostable multivibrator means 16 is comprised of a conventional circuit including transistors 162 and 166 wherein the collector electrode of transistor 166 is capacitively coupled to the base electrode of transistor 162 and the collector electrode of transistor 162 is resistively coupled to the base electrode of transistor 166. It is apparent therefore, that the stable output state of monostable multivibrator means 16 is attained when transistor 162 assumes its conducting state and conversely, the quasi-state output state is attained when transistor 166 assumes its conducting state. The collector electrode of transistor 166 is additionally coupled to one end of an energizing coil 169 of a first relay circuit, the other end of which is supplied with operating voltage +V. A moveable armature 170 of the relay circuit is magnetically controlled by the energizing coil 169 in the well-known manner. It is understood by those of ordinary skill in the art that the inductance of energizing coil-169 may contribute to the generation of injurious voltage transients capable of damaging transistor 166. Accordingly,- diode 168 is connected in shunt relationship with energizing coil 169 to absorb the transients.

The common junction of capacitance 146 and resistance 147 is coupled to monostable multivibrator 17 -to the base electrode of transistor 176. It is observed that the circuit comprising monostable multivibrator means 17 is identical to the circuit comprising monostable multivibrator means 16. Hence, the stable output state of monostable multivibrator means 17 is attained when transistor 172 assumes its conducting state and conversely, the quasistable output state is attained when transistor 176 assumes its conducting state. The

collector electrode of transistor 176 is additionally coupled to one end of an energizing coil 179 of a second relay circuit, the other end of which is supplied with operating voltage +V. A moveable armature 180 of the relay circuit is magnetically controlled by the energizing coil 179 in the well-known manner. Diode 178 is connected in shunt relationship 'with energizing coil 179 to absorb harmful transients that may be produced.

Clutch means l8 is herein illustrated as including a solenoid having an energizing coil 182 that is serially connectable to terminal 181 via moveable armature 170. Likewise clutch means 19 is illustrated as including a solenoid having an energizing coil 191 that is connectable to terminal 181 via moveable armature 180. The terminal 181 is adapted to be supplied with a source of energizing voltage whereby coils 182 and 191 may be selectively energized to thereby activate an associated clutch means.

Operation of the schematic diagram of FIG. 2 will now be described. If no obstruction is present to prevent light from impinging upon photoelectric sensing means 10, the intensity of the light received tends to reduce the impedance of the photoelectric sensing means to a minimal'value. Accordingly the voltage drop from terminal 103 to moveable contact 102 is much greater than the voltage drop across the low impedance of photoelectric sensing means 10. Hence moveable contact 102 applies a voltage less than the predetermined threshold level to the base electrode transistor 131 of Schmitt trigger means 13. Consequently transistor 131 assumes its nonconducting state thereby providing the collector electrode of transistor 131 with a high voltage potential. The high voltage potential is applied to the base electrode of transistor 136 whereby the latter transistor assumes its conducting state. Hence the collector electrode of transistor 136 is provided with a dc. voltage determined by the voltage divider network comprised of resistances 137 and 138. The dc. voltage is effectively blocked by capacitances 141 and 142 of pulse generating means 14 and the remaining circuitry of FIG. 2 maintains its quiescent state.

If the light path to photoelectric sensing means is now interrupted by the leading edge of a document, the impedance of the photoelectric sensing means tends to increase and the voltage drop thereacross rises above the predetermined threshold level. If desired, the photoelectric sensing means 10 may alternatively comprise a photodiode, a phototransistor, or the like, serially interposed between moveable contact 102 and resistance 104, and adapted to produce an increased output voltage in response to a decrease in the intensity of light impinging thereon. Application of the increased voltage to the base electrode of transistor 131 drives the transistor into its conducting state thereby diminishing the voltage at the collector electrode thereof. Accordingly, transistor 136 is urged to its nonconducting state and the collector electrode thereof is provided with a d.c. voltage substantially equal to the operating voltage +V. The positive d.c. voltage transition produced at the collector electrode of transistor 136 is coupled to diodes 143 and 144 by capacitances 141 and 142 respectively. The positive transition provides a forward bias on diode 144 and is shunted thereby to common conducting lead 105.. However, the positive transition provides a reverse bias on diode 143. Accordingly, capacitance 145 and resistance 150 function in the wellknown manner to differentiate the positive transition and transistor 151 is supplied with a positive pulse 148 at the base electrode thereof. The emitter follower configuration of transistor 151 applies a positive pulse to the base electrode of transistor 156. Transistor156 is arranged as a conventional inverting amplifier however, whereby the magnitude of the positive pulse applied to the base electrode thereof is amplified and the polarity of the pulse is inverted. Consequently a'negative pulse 159 is provided at the collector electrode of transistor 156. Negative pulse 159 is coupled to diode 161 and applied thereby as a triggering pulse to the base electrode of transistor 162 of monostable multivibrator means 16.

If it is assumed that the circuit parameters of the monostable multivibrator means 16 are suitably chosen, transistor 162 will assume its conducting state and transistor 166 will be cut 011' prior to the application of a triggering pulse-thereto. This, it is understood, corresponds to the stable output state of monostable multivibrator means 16 wherein a low voltage substantially equal to ground potential is provided at the collector electrode of transistor 162 and a high voltage below cutoff and the voltage provided at the collector electrode of transistor 162 increases. The voltage provided at the collector electrode of transistor 162 is supplied to the base electrode of transistor 166 by resistance 165. Hence, when the aforementioned voltage obtains the proper magnitude, transistor 166 is driven to its conducting state and the collector electrode thereof is provided with a voltage substantially equal to ground potential. Consequently, a series circuit is now provided from terminal 103 through energizing coil 169 through transistor 166 to the common conducting lead 105. The flow of current through coil 169 results in energization thereof causing moveable armature 170 to close. Closure of moveable armature 170 completes a series circuit from terminal 181 through the encrgization coil 182 of the solenoid included in clutch means 18. It is understood that transistor 166 will remain in its conducting state, i.e., monostable multivibrator means 16 will assume the quasi-stable output state thereof, for

only a finite time because the base electrode of transis tor 162 is connected to terminal 103 through resistance 164. Therefore, the voltage applied to the base electrode of transistor.162 will increase at a rate determined by the time constant of the monostable multivibrator means 16 which is a function of resistance 164 and capacitance 167, and when the applied voltage obtains the proper magnitude the monostable multivibrator means 16 will resume the stable output state thereof. Accordingly, current will no longer flow through coil 169, the moveable armature 170 will be opened and coil 182 will be de-energized. However, as has been previously described with reference to FIG. 1, if clutch means 18 includes a mechanical spring clutch member, energization of coil 182 will enable the clutch member to effect a complete rotation irrespective of the subsequent de-energization of the coil 182.

Obstruction of the light path to photoelectric sensing means 10 by the document to be reproduced maintains the impedance of the photoelectric sensing at a relatively high value. Accordingly the voltage applied to the base electrode of transistor 131 sustains the transistor 131 in its conducting state. Hence the dc. signal provided at the collector electrode of transistor 136 is characterized by a constant value substantially equal to the operating potential +V, to which pulse generating means 14 does not respond.

When the trailing edge of the document 12 is transported past the photoelectric sensing means 10, the impedance of the photoelectric sensing means is decreased in response to light impinging thereon. Accordingly the voltage supplied to the base electrode of transistor 131 by moveable contact 102 is less than the predetermined threshold level required to maintain the transistor in its conducting state. It is here noted that the predetermined threshold level may be adjusted by a corresponding adjustment of the moveable contact 102 of potentiometer 101 in the well-known manner. When transistor 131 assumes its nonconducting state, the voltage provided at the collector electrode thereof is substantially equal to the operating voltage +V, sufficient to drive transistor 136 into its conducting state. Consequently the dc. signal provided at the collector electrode of transistor 136 is decreased from the aforementioned first valve thereof to a second value thereof. This negative transition is coupled to diode 143 by capacitance 141 and to diode 144 by capacitance 142. The negative transition results in a forward bias of diode of 143 and is shunted thereby to common conducting lead 105. However, the negative transition provides a reverse bias on diode 144 whereupon the negative transition is difierentiated to produce negative pulse 149 at the common junction of capacitance 146 and resistance 147. It should be understood that the diode 143 effectively inhibits the differentiating circuit comprised of capacitance 145 and resistance 146.

Negative pulse 149 is applied to the base electrode of transistor 172 of monostable multivibrator means 17 by diode 171. The monostable multivibrator means 17 is triggered thereby into its quasi-stable output state. The manner of operation of the monostable multivibrator means 17 is identical to-that described hereinabove with respect to monostable multivibrator means 16 and therefore need not be set forth in detail herein. It is observed that when monostable multivibrator means 17 assumes the quasistable output state thereof, a series circuit is completed from terminal 103 through coil 179 through transistor 176 to the common conducting lead 105 thereby energizing coil 179 to close moveable armature 180. The closure of moveable armature 180 completes a series circuit from terminal 181 through the closed armature 180 to energizing coil 191 of a solenoid included in clutch means 19. Accordingly, the

through coil 179 to thereby open moveable armature 180, resulting in de-energization of the coil 191. At this time the schematic diagram of FIG. 2 is now prepared to respond to the leading and trailing edges of a subsequently transported document. It is clear fromthe foregoing explanation thereof, that monostable multivibrator means 16 and 17 cooperate with moveable armatures 170 and 180 and function as switch means which may be closed for predetermined periods of time to selectively connect coils 182 and 191 to the source of energy provided at terminal 181.

Another embodiment of the control system in accordance with the present invention is illustrated in FIG. 3 which comprises photoelectric sensing means 10, Schmitt trigger means 13, bistable means 31, pulse generating means 32 and 33, solenoid means 34 and 35, clutch means 18 and 19, and first and second mechanical programming means 21 and 22. Photoelectric sensing means is in optical communication with a source of light 1 1 as described hereinbefore with reference to FIG. 1 and is adapted to detect the leading and the trailing edges of a document 12 transported in the direction indicated by the arrow A. Photoelectric sensing means 10 is coupled to Schmitt trigger means 13, previously described, which in turn is coupled to bistable means 31. Bistable means 31 is characterized by first and second stable output states and is adapted to detect transitions in the signal supplied thereto by Schmitt trigger means 13. More specificallybistable means 31 is capable of assuming the first stable output state thereof, when the signal supplied thereto admits of a first level and to assume the second stable output state thereof when the signal supplied thereto admits of a second level. Hence bistable means 31 may comprise a conventional bistable multivibrator circuit, a flip-flop circuit, a two-position switch, a conventional relay circuit or the like. Bistable means 31 is provided with first and second output terminals wherein a signal is provided at the first'output terminal thereof in response to a detected positive transition in the signal supplied thereto; and a signal is provided at the second output terminal thereof in response to a detected negative transition in the signal supplied thereto.

Pulse generating means 32 is coupled to the first output terminal of bistable means 31 and is adapted to provide a pulse in response to a signal supplied thereto. Pulse generating means 32 may be similar to the aforedescribed pulse generating means 14 and therefore may comprise a conventional differentiating circuit, a unijunction transistor circuit, a univibrator, or the like. The second output terminal of bistable means 31 is coupled to pulse generating means 33 which is similar to just mentioned pulse generating means 32. The pulse generating means 32 and 33 are coupled to solenoid means 34 and 35, respectively, each of which solenoid means is adapted to be energized in response to a pulse generated by an associated pulse generating means. Solenoid means 34 and 35 are coupled .to clutch means 18 and 19 which are adapted to supply mechanical programming means 21 and 22 with the motor power derived from motor drive system 20 in the now understood manner previously described with respect to FIG. 1.

Operation of the apparatus represented by the block diagram of FIG. 3 will now be described. In the interest of brevity however, those components corresponding to previously described components of FIG. 1 will not be explained in detail. Photoelectric sensing means 10 supplies a signal that exceeds a predetermined threshold level to Schmitt trigger means 13 upon detecting the leading edge of document 12. Schmitt trigger means 13 is triggered to its first stable state in response to the signal supplied thereto thereby applying a d.c. signal admitting of a first level to bistable means 31. The signal supplied to bistable means 31 is characterized by a positive transition whereby bistable means 31 provides the first output terminal thereof with a signal. As will be described hereinafter the signal provided at the first output terminal of bistable means 31 is preferably a d.c. signal having a predetermined magnitude.

The signal provided at the first output terminal of bistable means 31 activates pulse generating means 32 to generate a positive pulse in response thereto, The generated pulse energizes solenoid means 34, such as by enabling the energizing coil of the solenoid means to be supplied with energy, thereby releasing the clutch means 18 to couple mechanical programming means 21 to motor drive system 20. Upon termination of the pulse generated by pulse generating means 32, solenoid means 34 is de-energized and the coupling between mechanical programming means 21 and motor drive system 20 is thence removed after one complete rotation of the cam assembly includable in the mechanical programming means.

Bistable means 31 provides a constant signal at the first output terminal thereof until photoelectric sensing means 10 detects the trailing edge of document 12.

Photoelectric sensing means 10 responds to the passing of the trailing edge of document 12 through the optical path defined by source of light 1 l and the photoelectric sensing means 10 by providing a signal of magnitude less than the predetermined threshold level to Schmitt trigger means 13'. Accordingly Schmitt trigger means 13 assumes its second state whereupon bistable means 31 is provided with a signal admitting of a second level.

Bistable means 31 assumes the second stableoutput state thereof in response to the negative transition in the signal supplied thereto. Consequently the signal provided at the first output terminal of bistable means 31 is terminated and the second output terminal thereof is provided with a dc. signal of predetermined magnitude. The signal provided at the second output terminal of bistable means 31 is applied to pulse generating means 33 whereupon a positive pulse is generated. The generated pulse is effective to energize solenoid means 35, such as by enabling the energizing coil of the solenoid means to be supplied with energy, such that clutch means 19 is released to couple mechanical programming means 22 to motor drive system 20. Solenoid means 35 is de-energized when the pulse generated by pulse generating means 33 terminates and the cam assemblyjincludable in mechanical programming means 32 effects one complete rotation. It is readily apparent that if desired, pulse generating means 32 and 33 may be replaced by a single conventional pulsing circuit having first and second output terminals coupled to solenoid means 34 and 35 respectively. ln addition the combination comprising bistable means 31, pulse generating means 32, and pulse generating means 33 may be replaced by a single conventional circuit adapted to generate pulses in response to transitions in the signal applied thereto. An exemplary circuit is disclosed at page 18 of the first edition of Electronics Handbook of Circuit Design published by McGraw- Hill, lnc. New York, New York.

A schematic diagram of a portion of the apparatus represented in FIG. 3 is illustrated in FIG. 4 and comprises photoelectric sensing means 10, Schmitt trigger means 13, bistable means 31, pulse generating means 32 and 33, and solenoid means 34 and 35. The photoelectric sensing means 10 and Schmitt trigger means 13 have been described in detail hereinabove. Accordingly, further description thereof is not deemed necessary for a complete understanding of the schematic illustration of FIG. 4. The collector electrode of transistor 136 of Schmitt trigger means 13 is coupled to the base electrode of transistor 312 of bistable means 31 by resistance 310. A biassing potential is applied to the base electrode of transistor 312 by resistance 311. Transistor 312 is arranged in a conventional relay driving circuit having a relay'coil 313 in the collector circuit thereof. As is understood transistor 312 may comprise a conventional switching transistor, well known to those of ordinary skill in the art. Relay coil 313 is magnetically coupled to a conventional relay armature 314 which, in turn, is connected to terminal 103. Relay armature 314 is adapted to contact first and second relay contacts 315 and 316 respectively, in accordance with the energization of relay coil 313. More specifically, energization of coil 313 enables relay armature 314 to complete a circuit from terminal 103 to relay contact 315. Conversely, de-energization of relay coil 313 enables relay armature 314 to complete a series circuit from terminal 103 to relay contact 316.

Relay contact 315 is connected to capacitance 322 of pulse generating means 32. A dc. current path from relay contact 315 to common conducting lead 105 is provided by resistance 321. Capacitance 322 is connected in series relationship with resistances 324 and 325 thereby forming a conventional differentiating circuit. Diode 323 is coupled from the common junction of capacitance 322 and resistance 324 to the common conducting lead and is suitably poled to inhibit the production of negative pulses. -T he common junction of resistances 324 and 325, which corresponds to the output terminal of a conventional differentiating circuit, is coupled to the base electrode of transistor 326. Transistor 326 is arranged in conventional relay driving configuration, similar to the configuration previously described with respect to transistor 312, and includes an energizing coil 327 of a relay circuit connected to the collector electrode thereof. Energizing coil 327 is magnetically coupled to moveable armature 328 which, in turn, is capable of completing a series circuit from terminal 341 to the activating coil 342 of a conventional solenoid means 34.

The second relay contact 316 of bistable means 31 is connected to capacitance 332 of pulse generating means 33. Pulse generating means 33 is similar to the aforementioned pulse generating means 32 and therefore includes a conventional differentiating circuit comprised of capacitance 332, resistance 334 and resistance 335 connected in series relationship. Diode 333 is connected from the common junction of capacitance 332 and resistance 334 to the common conducting lead 105 and is suitably poled to inhibit the production of negative pulses. The common junction of resistances 334 and 335 is connected to the base electrode of transistor 336 arranged in conventional relay driving configuration and including energizing coil 33'] connected to the collector electrode thereof. Energizing coil 337 is magnetically coupled to moveable armature 338 which is adapted to complete a series circuit from terminal 341 to activating coil 351 of the conventional solenoid means 35.

The operation of the apparatus represented by the schematic diagram illustrated in FIG. 4 will now be described. As is now understood detection of the leading edge of a document results in an increase in the impedance of photoelectric sensing means 10 and a corresponding increase in the voltage provided at the collector electrode of transistor 136. Hence Schmitt trigger means 13 assumes its first stable state and a signal admitting of a first level is provided at the collector electrode of transistor 137. One of ordinary skill in the art will recognize that photoelectric sensing means 10 may alternatively comprise a photodiode, a phototransistor or the like, interposed in series relationship between resistance 104 and moveable contact 102.

The signal provided at the collector electrode of transistor 136 is applied to the base electrode of transistor 312 and is of a magnitude sufficient to drive the latter transistor into its conducting state. Accordingly a series circuit is completed from terminal 103 through relay coil 313 through transistor 312 to the common conducting lead 105. Current flowing in the completed series circuit energizes the relay coil 313 to urge relay armature 314 into contact with relay contact 315. As a consequence thereof a series circuit is completed from terminal 103 through relay armature 314 to relay contact 315 to the common junction of resistance 321 When transistor 326 assumes its conducting state, a series circuit is completed from terminal 103 through energizing coil 327 through transistor 326 to the common conducting lead 105. The flow of current through the completed circuit energizes the energizing coil 327 to close moveable armature 328. The closure of armature 328 enables the activating coil 342 of solenoid means 34 to be supplied with energy applied to terminal 341. Solenoid means 34 is thus activated to release clutch means 18 as hereinabove described. Pulse 329 terminates after a brief duration thereof, whereupon transistor 326 returns to its non-conducting state. Accordingly, coil 327 is de-energized, moveable armature 328 is opened and solenoid means 34 is de-activated. It is recognized however, that the solenoid means 34 need be activated for only a brief interval of time to enable clutch means 18 to release.

Subsequent to the detection of the leading edge of a I document, light communication to photoelectric sensing means is interrupted and transistor 312 is maintained in its conducting state by the application of a signal admitting of a first level to the base electrode thereof. Hence, relay armature 314 remains in contact with relay contact 315 and capacitance 322 retains a constant voltage substantially equal to +V. Consequently, pulse generating means 32 does not provide further pulses. Upon detecting the trailing edge of a document however, the base electrode of transistor 131 is supplied with a signal that is less than the predetermined threshold level. Accordingly, Schmitt trigger means 13 assumes its second stable state and the signal provided at the collector electrode of transistor 136 is characterized by a negative transition from the first level to a second level. The decrease in magnitude of the voltage applied to the base electrode of transistor 312 is effective to switch said transistor into its nonconducting state. Hence current ceases to flow through relay coil 313 thereby de-energizing the coil and relay armature 314 is urged into contact with relay contact 316.

When relay armature 314 is removed from relay contact 315, the voltage stored by capacitance 322 disrupt the supply of energy to activating coil 351. The relay armature 314 ramains in contact with relay contact 316 and capacitance 332 retains a constant voltage substantially equal to +V. Consequently, pulse generating means 33 does not provide further pulses.

It is readily apparent from the foregoing explanation that moveable armature 328 and 338 of FIG. 4 correspond to the aforedescribed armatures 170 and 180 of FIG. 2. In addition, activating coils 342 and 351 correspond to aforedescribed coils 182 and 191. One of ordinary skill in the art will recognize that transistors 326 and 336 may be replaced by other conventional switching devices, such as silicon control switches or the like, adapted to selectively energize coils 327 and 337. Likewise, transistor 312 may be replaced by a conventional switching device for energizing coil 313 in accordance with the level of the signal produced by Schmitt trigger means 13. It is further recognized that the differentiating circuits illustrated in FIG. 2 and in FIG. 4 may be replaced by conventional operational amplifier differentiating means well known to those of ordinary skill in the art. Furthermore the Schmitt trigger means 13 and other conventional circuits illustrated herein may be comprised of conventional discrete components or of integrated circuits. Moreover the transistor elements utilized in the present invention are not limited to the n-p-n configurations illustrated but may include other conventional transistors such as p-n-p transistors, field effect transistors or the like.

While the invention has been particularly shown and described with reference to a plurality of embodiments thereof and a particular application thereof, it will be obvious to those of ordinary skill in the art that the charges through resistance 321 and rapidly decreases to provide a forward bias on diode 323. The diode thus provides a short circuit in shunt relationship with the differentiating circuit of. pulse generating means 32, thereby inhibiting the generation of a negative pulse. The completed series circuit from terminal 103 through relay armature 314 to relay contact 316 provides a rapidly increasing voltage at the common junction of resistance 331 and capacitance 332. This rapidly increasing voltage is differentiated by the differentiating circuit comprising pulse generating means 33 and a positive pulse 339 is applied to the base electrode of transistor 336. It is recognized that the positive pulse 339 applies a reverse bias on diode 333 which diode is now equivalent to an open circuit. Pulse 339, which admits of short duration, drives transistor 336 into its conducting state thereby completing a series circuit from terminal 103 through energizing coil 337 through transistor 336 to the common conducting lead 105. The energization of coil 337 closes moveable armature 338 whereby activating coil 351 of solenoid means 35 is supplied with energy from terminal 341. The termination of'pulse 339 returns transistor 336 to the nonconducting state thereof, and coil 337 is de-energized. Accordingly. moveable armature 338 is opened to interpresent invention'admits of general application with a device for performing operations upon sheets of material having variable length. The operations executed by the device may be individually performed or sequentially performed as described hereinabove. Moreover execution of the operations may be controlled by conventional controlling means such as the mechanical controlling means aforedescribed, or electrical controlling means well known to those skilled in the art. Therefore the foregoing and various other changesv and modifications in form and details may be made without departing from the spirit and scope of the invention. Consequently, it is intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

1. A control system for regulating the performance of predetermined sequences of operations by an electrophotographic reproducing device wherein said predetermined sequences are performed in time delayed relationship, said time delay being defined by the length of a document to be reproduced, comprising:

photoelectric sensing means for sensing the leading and trailing edges of a document to be reproduced; pulse generating means coupled to said photoelectric sensing means for generating a first pulse when said photoelectric sensing means senses the leading edges of a document and for generating a second pulse when said photoelectric sensing means senses the trailing edge of a document, saidpulse generating means comprising triggerable bistable means adapted to assume a first stable state when a signal applied thereto exceeds a predetermined threshold level and to assume a second stable state when a signal applied thereto is less than said predetermined threshold level; and

transition detecting means coupled to said triggerable bistable means for detecting each transition in the state assumed by said triggerable bistable means whereby said first pulse is generated when said triggerable bistable means assumes. said first state and said second pulse is generated when said triggerable bistable means assumes said second state;

first switch means coupled to said pulse generating means and responsive to said first pulse for initiating a first predetermined sequence of operations, said first switch means including first bistate means coupled to said pulse generating means and adapted to assume a first state in response to said first pulse, and first electromagnetic means coupled to said first bistate means and adapted to be energized when said first bistate means assumes said first state, whereby the energization of said first electromagnetic means enables first mechanical means to establish said first predetermined semeans to establish said second predetermined sequence of operations. 2. A control system in accordance with claim 1 wherein said triggerable bistable meanscomprises 7 Schmitt trigger means whereby said first stable state is represented by a signal admitting of afirst level and said second stable state is'represented by a signal admitting of a second level.

3. A control system in accordance with claim 2 wherein said transition detecting means comprises differentiating means responsive to transitions in the level of a signal applied thereto.

4. A control system in accordance with claim 3 wherein said first and second bistate means comprise first and second monostable multivibrator means, respectively, each of said monostable multivibrator means being adapted to assume the quasistable output state thereof in response to a pulse applied thereto.

5. A control system in accordance with claim 4 wherein said first and second electromagnetic means comprise:

first and second relay means, respectively, each of said first and second relay means including an energizing coil and a moveable contact, said moveable contact being adapted to complete a series circuit; and first and second solenoid means including first and second activating coils serially connectable to a source of energy via said first and second moveable contacts, respectively. 6. A control system in accordance with claim 2 wherein said transition detecting means comprises:

bistable circuit means having first and second stable output states and adapted to assume the first stable output state thereof in response to an applied signal admitting of a first level and to assume the second stable output state thereof in response to an applied signal admitting of a second level; and differentiating means responsive to transitions in the output state assumed by said bistable circuit means. 7. A control system in accordance with claim 6 wherein said first and second bistate means comprise: first and second relay means, respectively, each of said first and second relay means including an energizing coil and a moveable armature, said moveable armature being adapted to complete a series circuit; and

first and second switch means coupled to said differentiating means and responsive to pulses applied thereto for energizing said first and second energizing coils, respectively. I

8. A control system in accordance with claim 7 wherein said first and second electromagnetic means comprise first and second solenoid means including first and second activating coils serially connectable to a source of energy via said first and second moveable armatures, respectively. r

9. A control system in accordance with claim 8 wherein said bistable circuit means comprises:

a relay coil;

a switch having a control terminal for selectively energizing said relay coil'when a signal admitting of a first level is applied to said control terminal; and

a relay armature connected to a voltage source and adapted to contact a first relay contact when said relay coil is energized and to contact a second relay contact when said relay coil is de-energized.

10. A control system in accordance with claim 9 wherein said differentiating means comprises:

a first differentiator coupled to said first relay contact for generating said firstpulse when said relay armature contacts said first relay contact; and

a second differentiator coupled to said second relay contact for generating said second pulse when said relay armature contacts said second relay contact.

1 1. in a device for performing operations upon sheets of material having variable lengths wherein said operations are sequentially performed under the control of mechanical controlling means, apparatus for activating the mechanical controlling means, comprising: i

photocell means for sensing the leading and trailing edges of a sheet of material upon which said device operates, said photocell means being spaced from and in optical communication with a source of light for producing a signal in accordance with the intensity of light communicated thereto, the space defined by said photocell means and said source of light being adapted to receive said sheet of material;

Schmitt trigger means coupled to said photocell means for generating a signal admitting of a first level whensaid signal produced by said photocell means exceeds a threshold level and for generating a signal admitting of a second level when said signal produced by said photocell means is less than said threshold level;

pulse generating means having an input terminal coupled to said Schmitt trigger means and first and secnd output terminals for generating a first pulse at said first output terminal when the signal generated by said Schmitt trigger admits of a transition from said second level to said first level and for generating a second pulse at said second output terminal when the signal generated by said Schmitt trigger admits of a transition from said first level to said second level;

first switch means coupled to said first output terminal and responsive to said first pulse for completing a first series circuit;

second switch means coupled to said second output terminal and responsive to said second pulse for completing a second series circuit;

first solenoid means including an energizing coil serially connected to a source of energy via said first series circuit whereby said first solenoid means enables first clutch means to activate said mechanical controlling means, and

second solenoid means including an energizing coil serially connectable to a source of energy via said second series circuit whereby said second solenoid means enables second clutch means to activate said mechanical controlling means.

12. The apparatus of claim 11 further including first monostable multivibrator means interposed between said first switch means and said first output terminal for controlling said first switch means whereby said first series circuit is completed for a period of time determined by the time constant of said first monostable multivibrator means; and second monostable multivibrator means interposed between said second switch means and said second output terminal for controlling said second switch means whereby said second series circuit is completed for a period of time determined by the time constant of said second monostable multivibrator means. 

1. A control system for regulating the performance of predetermined sequences of operations by an electrophotographic reproducing device wherein said predetermined sequences are performed in time delayed relationship, said time delay being defined by the length of a document to be reproduced, comprising: photoelectric sensing means for sensing the leading and trailing edges of a document to be reproduced; pulse generating means coupled to said photoelectric sensing means for generating a first pulse when said photoelectric sensing means senses the leading edges of a document and for generating a second pulse when said photoelectric sensing means senses the trailing edge of a document, said pulse generating means comprising triggerable bistable means adapted to assume a first stable state when a signal applied thereto exceeds a predetermined threshold level and to assume a second stable state when a signal applied thereto is less than said predetermined threshold level; and transition detecting means coupled to said triggerable bistable means for detecting each transition in the state assumed by said triggerable bistable means whereby said first pulse is generated when said triggerable bistable means assumes said first state and said second pulse is generated when said triggerable bistable means assumes said second state; first switch means coupled to said pulse generating means and responsive to said first pulse for initiating a first predetermined sequence of operations, said first switch means including first bistate means coupled to said pulse generating means and adapted to assume a first state in response to said first pulse, and first electromagnetic means coupled to said first bistate means and adapted to be energized when said first bistate means assumes said first state, whereby the energization of said first electromagnetic means enables first mechanical means to establish said first predetermined sequence of operation, and second switch means coupled to said pulse generating means and responsive to said second pulse for initiating a second predetermined sequence of operations, said second switch means comprising, second bistate means coupled to said pulse generating means and adapted to assume a first state in response to said second pulse, and second electromagnetic means coupled to said second bistate means and adapted to be energized when said second bistate means assumes said first state, whereby the energization of said second electromagnetic means enables second mechanical means to establish said second predetermined sequence of operations.
 2. A control system in accordance with claim 1 wherein said triggerable bistable means comprises Schmitt trigger means whereby said first stable state is represented by a signal admitting of a first level and said second stable state is represented by a signal admitting of a second level.
 3. A control system in accordance with claim 2 wherein said transition detecting means comprises differentiating means responsive to transitions in the level of a signal applied thereto.
 4. A control system in accordance with claim 3 wherein said first and second bistate means comprise first and second monostable multivibrator means, respectively, each of said monostable multivibrator means being adapted to assume the quasistable output state thereof in response to a pulse applied thereto.
 5. A control system in accordance with claim 4 wherein said first and second electromagnetic means comprise: first and second relay means, respectively, each of said first and second relay means including an energizing coil and a moveable contact, said moveable contact being adapted to complete a series circuit; and first and second solenoid means including first and second activating coils serially connectable to a source of energy via said first and second moveable contacts, respectively.
 6. A control system in accordAnce with claim 2 wherein said transition detecting means comprises: bistable circuit means having first and second stable output states and adapted to assume the first stable output state thereof in response to an applied signal admitting of a first level and to assume the second stable output state thereof in response to an applied signal admitting of a second level; and differentiating means responsive to transitions in the output state assumed by said bistable circuit means.
 7. A control system in accordance with claim 6 wherein said first and second bistate means comprise: first and second relay means, respectively, each of said first and second relay means including an energizing coil and a moveable armature, said moveable armature being adapted to complete a series circuit; and first and second switch means coupled to said differentiating means and responsive to pulses applied thereto for energizing said first and second energizing coils, respectively.
 8. A control system in accordance with claim 7 wherein said first and second electromagnetic means comprise first and second solenoid means including first and second activating coils serially connectable to a source of energy via said first and second moveable armatures, respectively.
 9. A control system in accordance with claim 8 wherein said bistable circuit means comprises: a relay coil; a switch having a control terminal for selectively energizing said relay coil when a signal admitting of a first level is applied to said control terminal; and a relay armature connected to a voltage source and adapted to contact a first relay contact when said relay coil is energized and to contact a second relay contact when said relay coil is de-energized.
 10. A control system in accordance with claim 9 wherein said differentiating means comprises: a first differentiator coupled to said first relay contact for generating said first pulse when said relay armature contacts said first relay contact; and a second differentiator coupled to said second relay contact for generating said second pulse when said relay armature contacts said second relay contact.
 11. In a device for performing operations upon sheets of material having variable lengths wherein said operations are sequentially performed under the control of mechanical controlling means, apparatus for activating the mechanical controlling means, comprising: photocell means for sensing the leading and trailing edges of a sheet of material upon which said device operates, said photocell means being spaced from and in optical communication with a source of light for producing a signal in accordance with the intensity of light communicated thereto, the space defined by said photocell means and said source of light being adapted to receive said sheet of material; Schmitt trigger means coupled to said photocell means for generating a signal admitting of a first level when said signal produced by said photocell means exceeds a threshold level and for generating a signal admitting of a second level when said signal produced by said photocell means is less than said threshold level; pulse generating means having an input terminal coupled to said Schmitt trigger means and first and second output terminals for generating a first pulse at said first output terminal when the signal generated by said Schmitt trigger admits of a transition from said second level to said first level and for generating a second pulse at said second output terminal when the signal generated by said Schmitt trigger admits of a transition from said first level to said second level; first switch means coupled to said first output terminal and responsive to said first pulse for completing a first series circuit; second switch means coupled to said second output terminal and responsive to said second pulse for completing a second series circuit; first solenoid means including an energizing coil serially connected to a sOurce of energy via said first series circuit whereby said first solenoid means enables first clutch means to activate said mechanical controlling means, and second solenoid means including an energizing coil serially connectable to a source of energy via said second series circuit whereby said second solenoid means enables second clutch means to activate said mechanical controlling means.
 12. The apparatus of claim 11 further including first monostable multivibrator means interposed between said first switch means and said first output terminal for controlling said first switch means whereby said first series circuit is completed for a period of time determined by the time constant of said first monostable multivibrator means; and second monostable multivibrator means interposed between said second switch means and said second output terminal for controlling said second switch means whereby said second series circuit is completed for a period of time determined by the time constant of said second monostable multivibrator means. 